ARTICLE IN PRESS

1352-2310/$ - se

doi:10.1016/j.at

�CorrespondE-mail addr

1Permanent a

Beijing 100091,

Atmospheric Environment 40 (2006) 7963–7974

www.elsevier.com/locate/atmosenv

Ozone pollution and ozone biomonitoring in European cities.Part I: Ozone concentrations and cumulative exposure indices

at urban and suburban sites

Andreas Klumppa,�, Wolfgang Ansela, Gabriele Klumppa, Vicent Calatayudb,Jean Pierre Garrecc, Shang Hec,1, Josep Penuelasd, Angela Ribasd,

Helge Ro-Poulsene, Stine Rasmussene, Marıa Jose Sanzb, Phillippe Vergnef

aInstitute for Landscape and Plant Ecology and Life Science Center, University of Hohenheim, 70599 Stuttgart, GermanybFundacion CEAM, Parque Tecnologico, c/ Charles Darwin 14, 46980 Paterna (Valencia), Spain

cINRA Nancy, Laboratoire Pollution Atmospherique, 54280 Champenoux, FrancedUnitat d’Ecofisiologia CSIC-CEAB-CREAF, Centre de Recerca Ecologica i Aplicacions Forestals (CREAF), Universitat Autonoma de

Barcelona, 08193 Bellaterra (Barcelona), SpaineBotanical Institute, University of Copenhagen, Øster Farimagsgade 2D, 1353 Copenhagen K, Denmark

fENS Lyon and Lyon Botanical Garden, 46 Allee d’Italie, 69364 Lyon Cedex 07, France

Received 16 December 2005; accepted 4 July 2006

Abstract

In the frame of a European research project on air quality in urban agglomerations, data on ozone concentrations from

23 automated urban and suburban monitoring stations in 11 cities from seven countries were analysed and evaluated.

Daily and summer mean and maximum concentrations were computed based on hourly mean values, and cumulative

ozone exposure indices (Accumulated exposure Over a Threshold of 40 ppb (AOT40), AOT20) were calculated. The

diurnal profiles showed a characteristic pattern in most city centres, with minimum values in the early morning hours, a

strong rise during the morning, peak concentrations in the afternoon, and a decline during the night. The widest

amplitudes between minimum and maximum values were found in central and southern European cities such as

Dusseldorf, Verona, Klagenfurt, Lyon or Barcelona. In the northern European cities of Edinburgh and Copenhagen, by

contrast, maximum values were lower and diurnal variation was much smaller. Based on ozone concentrations as well as

on cumulative exposure indices, a clear north–south gradient in ozone pollution, with increasing levels from northern and

northwestern sites to central and southern European sites, was observed. Only the Spanish cities did not fit this pattern;

there, ozone levels were again lower than in central European cities, probably due to the direct influence of strong car

traffic emissions. In general, ozone concentrations and cumulative exposure were significantly higher at suburban sites than

at urban and traffic-exposed sites. When applying the newly established European Union (EU) Directive on ozone

pollution in ambient air, it was demonstrated that the target value for the protection of human health was regularly

surpassed at urban as well as suburban sites, particularly in cities in Austria, France, northern Italy and southern

e front matter r 2006 Elsevier Ltd. All rights reserved.

mosenv.2006.07.017

ing author. Tel.: +49711 4593043; fax: +49 711 4593044.

ess: aklumpp@uni-hohenheim.de (A. Klumpp).

ddress: Chinese Academy of Forestry, Research Institute of Forest Ecology and Environmental Science, Wan Shou Shan,

PR China.

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747964

Germany. European target values and long-term objectives for the protection of vegetation expressed as AOT40 were also

exceeded at many monitoring sites.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Air quality; AOT40; Thresholds; EU Directive; Urban air pollution

1. Introduction

In most European cities, air quality has substan-tially improved over the last decades due to stricterlegal regulations, the adoption of less-pollutingtechnologies and the relocation of industry fromthe city centres. Nevertheless, air pollution remainsone of the most urgent environmental problems inEurope. The enduring unsatisfactory situation ofurban air quality originates mainly from the steadilyincreasing road traffic. According to the EuropeanEnvironment Agency (EEA) (2003), air pollution inEurope continues to pose risks and to have adverseeffects on human health and on natural and man-made environments. Considerable fractions ofurban populations are regularly exposed to peakair pollution in excess of current limit values. Inparticular, health effects caused by suspendedparticulate matter and by ozone and other photo-oxidants are presently the focus of public andscientific interest.

Projections from the Auto-Oil II air quality study(De Leeuw, 2002) indicate that reductions in theemissions of ozone precursors will significantlyreduce regional ozone production and peak con-centrations. Air quality is therefore expected toimprove in the period until 2010, but the improve-ments will be insufficient to meet the air qualitytargets all over Europe. On the other hand, there isgrowing evidence that sources outside Europe arebecoming more important and that backgroundozone concentrations are generally increasing on thenorthern hemisphere (Prather et al., 2003; Grenn-felt, 2004). Moreover, due to the complex chemicalreactions and vertical transport processes in theatmosphere, a strong temporal and spatial varia-bility of ozone pollution exists; this leads to rapidlyalternating episodes of elevated and low ozonelevels and often to significant differences in ozoneload of urban vs. suburban and rural areas(Garland and Derwent, 1979; Fenger, 1999). Inview of these special features, ozone and itspotential impact on human health and the environ-ment will stay on the agenda of European environ-mental policy in the future.

The assessment and management of air quality inMember States of the European Union is regulatedby the Air Quality Framework Directive (EuropeanUnion (EU), 1996) and its so-called DaughterDirectives. Limit values for the protection of humanhealth and for the protection of vegetation fromharmful ozone concentrations have been settled byDirective 2002/3/EC relating to ozone in ambientair (European Union (EU), 2002), which wasimplemented in 2003. Measurements of atmosphericpollutant concentrations as prescribed by Europeandirectives and national legislation, however, provideno direct information regarding the possible pollu-tion effects on man and the environment becausethe reaction of an organism depends not only onpollutant concentrations and exposure duration,but is also influenced by a range of predisposing oraccompanying factors. Hence, biomonitoring usinghighly sensitive plant species and cultivars is anappropriate means to detect and to monitor airpollution effects; this supplements informationgained from conventional pollution measurementsand modelling.

EuroBionet, the ‘European Network for theAssessment of Air Quality by the Use of Bioindi-cator Plants’ was established in 1999 as a network ofresearch institutes and municipal environmentalauthorities from 12 urban agglomerations in eightEU Member States. It aimed at promoting environ-mental awareness of the urban population and atassessing and evaluating air quality by applyinghighly standardised bioindication methods. To thisend, about 100 biomonitoring sites were establishedand operated over a period of up to 3 years. In orderto comparatively evaluate air quality based on airpollution as well as on biological effects data, somebioindicator stations were established close toautomated air monitoring stations (Klumpp et al.,2002, 2004).

The present paper reports on ambient ozonepollution in urban and suburban areas using dataobtained by conventional monitoring of atmosphericozone concentrations as well as by standardisedexposure of ozone-sensitive tobacco plants. Part Ifocuses on data gained by routine measurements of

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–7974 7965

ozone concentrations and evaluates them based oncurrent European legislation. In an anticipatoryapproach, we used the new Ozone Directive (EU,2002) for this purpose although it came into force onlyafter the project’s end. This approach enabled us todetermine whether the new target values and long-term objectives for human health and protection ofvegetation can be met in European cities and wherethese limits are exceeded. This also improves ourknowledge about the occurrence of ozone episodes inlarge agglomerations. In Part II (Klumpp et al.,2006b), we report on the intensity and geographicaldistribution of ozone-induced injuries to bioindicatorplants and on the relationship between ambient ozonelevels and ozone-induced effects on plants.

2. Material and methods

2.1. The city network

The present study was part of the European bio-indicator programme EuroBionet (www.eurobionet.com), which aimed at assessing and evaluatingair quality in 12 urban agglomerations throughoutEurope using various bioindicator species (Klumppet al., 2002, 2004). To this end, a network ofmunicipal administrations and research instituteswas established under the coordination ofthe University of Hohenheim in 1999. Theproject started with the following cities and regionsas participants: Copenhagen (Denmark), Edinburgh(UK), Klagenfurt (Austria), Greater Lyon (France),Sheffield (UK), and Verona (Italy). The City ofDusseldorf (Germany), the City of Ditzingen/Greater Stuttgart (Germany), Greater Nancy(France) and the regional government of Catalonia/Barcelona (Spain) joined the network in 2000, thecities of Valencia (Spain) and Glyfada/GreaterAthens (Greece) in 2001. In each city, localbioindicator networks including urban, suburban,industrial, traffic and reference sites were implemen-ted, totalling about 100 stations in operation during1999–2002 (cp. Klumpp et al., 2006b). Classificationand location of sampling points were in conformitywith the criteria established by EU (2002).

2.2. Measurement and evaluation of ambient ozone

concentrations

In order to comparatively evaluate air qualityusing air pollution and biomonitoring data withinthe local networks, some bioindicator stations were

established close to continuously working airmonitoring stations (Table 1) run by the local andregional authorities in charge of air pollutionmonitoring. Ozone concentrations were measuredat 2.5–3.5m above ground by the UV photometricmethod according to EU (2002) using automatedanalysers from different manufacturers and wereprovided as hourly or half-hourly mean values. Thepaper focuses on 2001 because in that year almostcomplete data sets were available from 11 out of 12cities. No data on atmospheric ozone concentra-tions in Glyfada were available: the values fromneighbouring Athens were not used as they were notconsidered representative for the Glyfada suburb.

24-h mean and maximum ozone concentrationswere calculated based on the hourly mean values.Additionally, mean and mean daily maximumvalues as well as average daily profiles of ozoneconcentrations were computed for the eight bi-weekly exposure periods of tobacco plants (cp.Klumpp et al., 2006b) and for the periods May–Julyand April–September. A cumulative ozone exposureindex, the Accumulated exposure Over a Thresholdof 40 ppb (AOT40; expressed as ppb*h), wascalculated as the sum of the differences betweenthe hourly ozone concentrations exceeding 40 ppband 40 ppb using only the hourly values measuredbetween 08:00 and 20:00 h CET daily for the periodsbetween May–July and April–September accordingto the Ozone Directive (EU, 2002). Since sensitiveplant species and cultivars may develop character-istic injuries even at ambient levels below 40 ppb,the AOT20 was also determined (correspondingly tothe AOT40 calculation). Additionally, annual meanvalues of NO2 concentrations are given in order todescribe the general air pollution situation at themonitoring sites (cp. Table 2).

The evaluation of ozone concentrations andexposure characteristics included the count ofexceedances of: (i) target values and long-termobjectives for the protection of the vegetation(9000 and 3000 ppb*h during May–July, respec-tively) and forests (10,000 ppb*h during April–September); (ii) the target value for the protectionof human health (60 ppb as maximum daily 8-hmean, not to be exceeded at more than 25 days/year); and (iii) the information and alert thresholds(90 and 120 ppb hourly means), as prescribed by EU(2002). The AOT40 values of 3000 and10,000 ppb*h correspond to the ‘Critical Levels’for the protection of crops and forests establishedby United Nations Economic Commission for

ARTICLE IN PRESS

Table 1

Location and characteristics of ozone monitoring stations and corresponding bioindicator sites

City/code Name of air monitoring/bioindicator station Distance between both stations (m) Type

Edinburgh/Ed Princes Street/Donaldson’s College 2000 Urbanb

Sheffield/Sh City Centre/Heeley Farm 1500 Urbanb

Copenhagen/Co Jaegersborg/Jaegersborg 20 Suburban

Jagtvej/Assistens Kirkegard 400 Urbanb

Lille Valby/Lille Valby 10 Suburban

Dusseldorfa/Du Lorick/Strandbad Lorick 70 Suburbanb

Nancy/Na Brabois/Airlor 70 Suburban

Tomblaine/Meteo France 70 SuburbanViaduc Kennedy/Parc Ste. Marie 600 Urbanb

Stuttgarta/St Hohenheim/Hohenheim 5 SuburbanPlochingen/Plochingen 450 Suburban

Klagenfurt/Kl KoschatstraXe/KoschatstraXe o5 Urbanb

Lyon/Ly St. Just/St. Just o5 UrbanCroix Luizet/Croix Luizet o5 Urban

Gerland/Gerland 800 Urbanb

Veronaa/Ve Torricelle/San Mattia 700 Suburban

ZAI/Liceo Galilei 40 Suburbanb

Barcelona/Ba Bellaterra/Bellaterra 5000 Suburban

Gracia/Gracia o5 UrbanHospitalet/Sants o5 Urbanb

Valencia/Va Avda. Aragon/Avda. Aragon o5 Urban/streetNuevo Centro/Prof. Beltran Baguena o5 Urban/streetb

GVF Catolico/GVF Catolico o5 Urban/street

aNo O3 concentrations from urban air monitoring stations available.bSites considered for presentation of diurnal profiles in Fig. 1.

A. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747966

Europe (UNECE) (Karenlampi and Skarby, 1996)and World Health Organization (WHO) (2000),whereas the 8-h mean of 60 ppb corresponds to thecritical level for human health (WHO, 2000).

2.3. Quality assurance and control

Ozone monitoring equipment was maintained andcalibrated by the responsible authorities according tothe state-of-the-art. Following the Ozone Directive(EU, 2002), at least 75% of valid data are required tocalculate mean values and 90% to compute cumula-tive indices and number of threshold exceedances. Inour study, the proportion of valid data was generallybetween 90% and 100%, except from one stationwhere a proportion of about 85% was accepted.Missing data were not estimated when computingAOT40 values. Monitoring sites with less than 85%valid data were excluded from the calculations.

3. Results and discussion

3.1. Diurnal ozone cycles

The diurnal profiles of ozone concentrationsshowed a characteristic pattern in most city centres,

with minimum values in the early morning, a strongrise during the morning with increasing solarradiation, peak concentrations in most cities in theafternoon between 15.00 and 17.00 h, and a declinedue to ozone destruction by nitrogen oxide duringthe night (Fig. 1). This feature can be explained bythe activating role of solar radiation in photoche-mical ozone generation in the mixing layer andozone transport from upper atmospheric layers.Once the nocturnal inversion layer has beenestablished, no major changes in ozone concentra-tions occur until rupture of inversion layers andphotochemical reactions start again with beginningof the daylight period (Coyle et al., 2002; Duenaset al., 2002). The widest amplitudes betweenminimum and maximum concentrations were foundin central and southern European cities such asDusseldorf, Verona, Klagenfurt, Lyon or Barcelona.Maximum values were lower and diurnal variationwas much smaller in the northern European citiesof Edinburgh and Copenhagen. There, slightlyhigher ozone values were also measured in thenight and early morning hours before start ofthe rush hour. In Edinburgh, the mean dailymaximum even occurred at 04:00 h. With low totalphotochemical activity in northern cities, vertical

ARTICLE IN PRESS

Table

2

Meanandmeandailymaxim

um

O3concentrationsaswellasAOT20andAOT40values

duringMay–July

andApril–September

2001;annualmeanvalues

ofNO

2

Sitecharacteristics

and

names

Ozone:

May–July

Ozone:

April–September

NO

2

AOT40

(ppb*h)

AOT20

(ppb*h)

Mean7s.d.(ppb)Meandaily

maxim

um7s.d.

(ppb)

AOT40

(ppb*h)

AOT20

(ppb*h)

Mean7s.d.(ppb)Meandaily

maxim

um7s.d.

(ppb)

Annualmean

(ppb)

Urb

an

site

s

EdPrincesStreet

80

2816

17.876.2

29.678.6

91

4860

16.876.6

28.478.8

22.4

ShCityCentre

387

6004

20.976.2

33.378.7

411

9360

19.377.0

31.079.0

19.2

CoJagtvej

540

10,036

24.876.5

36.777.3

598

13,798

21.677.4

33.878.0

20.8

NaViad.Kennedy

5866

18,608

29.1710.0

47.3715.8

8301

29,051

26.479.3

43.6715.7

21.3

KlKoschatstraXe

10,644

29,162

35.378.0

56.6710.8

17,219

49,320

31.2710.4

52.9713.9

14.0

LySt.Just

9660

25,432

32.9710.2

56.4718.6

13,722

40,358

29.2710.7

50.8718.2

19.8

LyGerland

9392

24,094

32.4710.6

56.2717.7

13,172

37,297

28.6710.9

51.1717.7

23.9

LyCroix

Luizet

6023

19,124

28.279.4

50.9716.4

9136

31,723

24.979.6

46.5716.0

21.8

BaHospitalet

4926

19,653

28.476.7

50.5710.3

6881

34,688

26.977.0

47.279.8

20.8

BaGracia

1373

8420

19.176.7

40.0711.4

1548

13,310

17.976.4

36.6710.1

33.3

VaNuevoCentro

1413

10,765

22.375.9

40.7710.7

2452

20,166

21.976.0

40.7710.1

26.0

VaGVFCatolico

242

4581

18.774.5

33.677.6

278

8332

17.674.5

32.177.2

33.3

VaAvda.Aragon

120

3714

15.574.5

29.379.2

243

7290

15.175.1

28.979.3

41.1

Sub

urb

an

site

s

CoLille

Valby

1152

16,475

29.674.6

39.976.8

2306

29,236

28.575.4

39.378.1

5.2

CoJaegersborg

3350

19,962

33.576.2

46.478.3

5650

34,450

31.277.6

44.279.9

n.d.

DuLorick

5757

18,696

27.978.3

50.3716.0

8071

29,008

24.279.6

44.1718.3

15.6

NaBrabois

11,631

29,268

35.8710.2

56.1717.5

15,403

45,771

32.4710.0

50.5717.0

12.0

NaTomblaine

10,846

28,557

35.279.1

55.3716.2

15,024

45,767

31.479.3

50.2716.2

9.4

StHohenheim

10,370

27,506

35.179.2

55.6716.9

14,832

45,508

31.1710.1

50.5716.8

n.d.

StPlochingen

15,722

31,689

30.4711.8

64.7723.4

19,428

44,970

24.4712.1

54.0723.3

18.7

VeZAI

16,173

34,871

37.3710.7

65.5715.5

25,292

57,423

32.2713.0

59.7718.2

31.2

VeTorricelle

13,838

30,690

45.0712.0

62.9714.3

21,837

51,685

40.7715.0

56.8718.1

9.4

BaBellaterra

7094

21,731

29.376.7

54.7711.3

9723

37,848

26.477.1

49.7711.0

n.d.

ExceedancesofEU

ozonetarget

values

fortheprotectionofvegetation(9000ppb*h)andforests(10,000ppb*h)in

bold;sd¼

standard

deviation;n.d.¼

notdetermined.

A. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–7974 7967

ARTICLE IN PRESS

0

10

20

30

40

50

60

70

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

11:0

0

12:0

0

13:0

0

14:0

0

15:0

0

16:0

0

17:0

0

18:0

0

19:0

0

20:0

0

21:0

0

22:0

0

23:0

0

24:0

0

Ozo

ne c

once

ntra

tion

[ppb

]

EdinburghSheffieldCopenhagenDüsseldorfNancyKlagenfurtLyonVeronaBarcelonaValencia

Fig. 1. Mean daily profile of ozone concentrations at selected urban and suburban (Dusseldorf/Verona) monitoring sites (cp. Table 1)

over the period April–September 2001.

Table 3

Results of one-way ANOVA using site type (urban/suburban) as

a factor

Ozone parameter Significance (p)

Mean value May–July o0:01Mean maximum May–July o0:01AOT40 May–July o0:001Mean value April–September o0:01Mean maximum April–September o0:01AOT40 April–September o0:01

A. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747968

exchange processes and onshore breezes in coastalregions that entrain ozone-polluted airmasses dur-ing the night and consequently lead to little night-time depletion of ozone (Garland and Derwent,1979; Coyle et al., 2002) play a comparativelygreater role than they do in central and southernEurope, where higher photochemical ozone produc-tion rates and re-circulation of ozone-rich airmassesprevail (Duenas et al., 2002; Millan et al., 2002;Sanz et al., 2004).

Within the local networks, suburban districtsgenerally featured higher concentrations during thedaylight hours than did the city centres; ozonebreakdown by nitrogen oxide at night and duringthe early morning was less evident than at the urbanstations (data not shown).

3.2. Ozone concentrations and cumulative ozone

exposure

24-h mean ozone concentrations over the periodMay–July varied between 15.5 ppb at the site‘Avenida Aragon’ in Valencia and 45 ppb at‘Torricelle’ in Verona, whereas the mean dailymaximum values ranged between 29.4 ppb at thesame Spanish site and 65.5 ppb at ‘ZAI’ in Verona(Table 2). Lowest mean and maximum concentra-tions were generally registered in northern Europe(UK and Denmark) and at several Spanish sites; thehighest levels occurred in Germany, France, Austriaand northern Italy. The highest hourly mean value

of the whole network (149.5 ppb) was measured at‘Plochingen’ southeast of Stuttgart on 31 July 2001.This was also the highest value measured inGermany in that year. Mean and maximum valuesfrom April to September were somewhat lower thanfrom May to July due to the relatively low ozonelevels in early spring and autumn, but they followeda similar geographical pattern. Urban and suburbansites differed significantly concerning ozone pollu-tion, with average values of 25.4 and 34.4 ppb andaverage maximum values of 43.0 and 56.8 ppb aturban and suburban sites, respectively; this wasvalid for the 3-month period and the longermonitoring period (Table 3). This well-knownphenomenon reflects the higher emissions of nitro-gen oxides in urban centres (cp. Table 2) and theconsequently more intense ozone quenching duringnighttime.

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–7974 7969

Differences between monitoring sites were muchmore pronounced when cumulative exposure indiceswere used for comparison. Accordingly, the AOT40(May–July) varied between 80 ppb*h at ‘PrincesStreet’ in Edinburgh and 10,644 ppb*h at ‘Koschat-straXe’ in Klagenfurt for urban stations, andbetween 1152 ppb*h at ‘Lille Valby’ in Copenhagenand 16,173 ppb*h at ‘ZAI’ in Verona for thesuburban stations (Table 2). Again, sites differedsignificantly depending on their location within theagglomerations (Table 3). Suburban sites featuredAOT40 values that were nearly three times higherthan those determined at urban sites.

The AOT40 values for the period April–September2001 revealed the same geographical pattern asthat in the already described shorter calculationperiod (Table 2). When compared to the periodMay–July, the cumulative ozone exposure increasedby up to 102%. At the urban sites in the northernEuropean cities Edinburgh, Sheffield and Copenha-gen and at some Spanish sites, AOT valuesincreased only minimally (6–14%) when extendingthe calculation period to the spring and late summermonths. A relatively high increase, by contrast, wasfound at suburban sites in Copenhagen and Veronaand at some urban sites in Klagenfurt, Lyon, andValencia. The monthly data revealed that the strongincreases in long-term cumulative values weremostly due to high ozone concentrations in August(Dusseldorf, Nancy, Klagenfurt, Lyon, Verona). InValencia, on the other hand, comparably highozone pollution already appeared in April, whilein Barcelona both months (April and August)showed similarly high values (data not shown).

Because of the high ozone sensitivity of tobaccocultivar Bel–W3, AOT20 values were also deter-mined. As Table 2 shows, the geographical pollu-tion pattern was still evident when the lower cut-offvalue was employed, even though the differencesbetween the individual cities were clearly reduced.

Based on ozone concentrations as well as oncumulative exposure indices, ozone pollution showeda clear north–south gradient, with increasing levelsfrom northern and northwestern sites to central andsouthern European sites. Only the two Spanish citiesof Barcelona and Valencia were exceptions (Table 2):their ozone levels were again lower than in centralEuropean cities like Verona or Klagenfurt. Fig. 2illustrates the AOT40 values from May to July 2001at urban and suburban sites in various cities.

The observed latitudinal gradient of ozone con-centrations and cumulative exposure indices was

further investigated by Pearson correlation andlinear regression analyses. Table 4 shows the resultsusing data of both urban and suburban sites butexcluding the two Spanish cities. Linear regressionfitted best to the data, and correlation coefficientswere significant for concentration as well as forAOT40 values. Highest correlation coefficients(R40.8) were obtained when maximum concentra-tions and AOT40 were computed against latitude ofsites. Similar results were published by Sanz et al.(2004), who analysed ozone concentrations at ruralsites in SW Europe during 2000–2002. In theirinvestigations, however, rural sites from variousSpanish regions also fitted well into the exponentialmodel they used.

The monitoring data from our network—withlow ozone levels at the Spanish sites—seem tocontradict not only Sanz et al. (2004) but alsovarious papers and reports from environmentalagencies that relate strong ozone pollution along theSpanish east coast. The western Mediterraneanbasin, with its intense solar radiation and highemission rates of ozone precursors, is known tosuffer from chronic ozone episodes during thesummer and is frequently described as a ‘largenatural photo-chemical reactor’ (Millan et al.,2000). This is due to the specific topographicalsituation and circulation dynamics of the region,where high mountain ranges surrounding the coast-al cities favour the isolation from frontal systemsand the creation of closed re-circulation processesdriven by sea breezes. The result is a system ofstacked layers of airmasses with high photochemicalactivity and comparatively long residence time ofthe polluted air (Millan et al., 2000, 2002; Gangoitiet al., 2001). Consequently, prolonged ozoneepisodes and exceedances of limit values for bothhuman health and vegetation are frequently re-ported from urban and rural areas along the Iberiancoast (Gimeno et al., 1995; EEA, 2001; Tobiasand Scotto, 2005). Strong ozone pollution exceedingthreshold values was also observed for exampleat several rural sites near Valencia during summer2001 (Mantilla et al., 2002) and in Catalonia(Ribas and Penuelas, 2003, 2004). The urbanmonitoring sites in our study, however, are locatedin the city centres of Barcelona and Valencia, quiteclose to heavy-trafficked roads and junctions. Suchsites are directly influenced by high car trafficemissions (Gimeno et al., 1995; Mantilla et al.,2002) and partly also by NOx emissions from majorindustrial sources (Toll and Baldasano, 2000)

ARTICLE IN PRESS

Table 4

Results of regression analyses of the relationships between latitude of monitoring sites and ozone exposure indices

Ozone parameter Correlation coefficient R R2 Significance of R

Mean value May–July 0.643 0.413 po0:01Mean maximum May–July 0.831 0.690 po0:001AOT40 May–July 0.813 0.661 po0:001Mean value April–September 0.558 0.311 po0:05Mean maximum April–September 0.832 0.692 po0:001AOT40 April–September 0.829 0.687 po0:001

80 387 540

5866

106449660 9392

60234926

1373 1413120 242

0

3000

6000

9000

12000

15000

18000

Ed Princes St.

Sh City Centre

Co Jagtvej

Na CUGN

Kl Koschatstr.

Ly St Just

Ly Gerland

Ly Croix Luizet

Ba Hospitalet

Ba Gracia

Va Prof. Báguena

Va Aragón

Va GVF Católico

AO

T40

[ppb

*h]

___EU Target Value

--- WHO-Guideline EU Long-term Objective

1152

3350

5757

1084611631

10370

15722

13838

16173

7094

0

3000

6000

9000

12000

15000

18000

Co Lille Valby

Co Jaegersborg

Dü Lörick

Na Tomblaine

Na Brabois

St Hohenheim

St Plochingen

Ve Torricelle

Ve ZAI

Ba Bellaterra

AO

T40

[ppb

*h]

___EU Target Value

--- WHO-Guideline EU Long-term Objective

(a)

(b)

Fig. 2. AOT40 values at urban (a) and suburban (b) monitoring stations (cp. Table 1) for the period May–July 2001 as well as target and

threshold values relating to vegetation protection as established by EU and WHO (cities listed from north to south).

A. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747970

resulting in elevated ambient levels of nitrogenoxides (cp. Table 2). The significant influence oftraffic emissions at these sites has also beendemonstrated by exposure of various bioindicatorspecies in our studies (Klumpp et al., 2004, 2006a).

Consequently, ozone is rapidly being depleted bythe high NO levels at those sites, and higherozone levels can only be found at more distantsites like the suburban station ‘Bellaterra’ inBarcelona.

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–7974 7971

3.3. Exceedance of European target values and long-

term objectives

Analysis of ozone data according to the newEuropean Ozone Directive (EU, 2002) demon-strated that the target value for protection ofhuman health (60 ppb as running 8-h mean) wassurpassed at urban as well as suburban sites in manycities, particularly in central and southern Europe,at least once a year (Table 5). In Lyon, Nancy,Klagenfurt, Stuttgart and Verona, this target valuewas exceeded on more than 25 days, which is thelimit permitted by the directive. At the sites ‘ZAI’and ‘Torricelle’ (Verona) and ‘Plochingen’ (Stutt-gart) the limit was even exceeded on more than 50days in the study year. Only at the urban sites ofEdinburgh, Sheffield, Copenhagen and Valenciaand at one of the urban sites in Barcelona did therunning 8-h average always remain below 60 ppbover the whole period April–September 2001.

Table 5

Exceedances of the thresholds for information and warning of the popul

the protection of human health (bold: surpassing the limit of 25 days as

(EU, 2002)

Site characteristics and names Information threshold 90 ppb

(days/hours)

Urban sites

Ed Princes Street 0

Sh City Centre 0

Co Jagtvej 0

Na Viaduc Kennedy 2/2

Kl KoschatstraXe 1/1

Ly St Just 5/19

Ly Gerland 5/11

Ly Croix Luizet 1/4

Ba Hospitalet 0

Ba Gracia 0

Va Nuevo Centro 0

Va GVF Catolico 0

Va Avda. Aragon 0

Suburban sites

Co Lille Valby 0

Co Jaegersborg 0

Du Lorick 4/13

Na Brabois 4/18

Na Tomblaine 2/10

St Hohenheim 3/9

St Plochingen 11/57

Ve ZAI 7/21

Ve Torricelle 8/27

Ba Bellaterra 0

The threshold for information to the public(90 ppb as 1-h mean) was also regularly exceededat the monitoring sites in France, Italy, andGermany, and once at the Austrian site. The highestnumber of exceedances (57 times) was registered at‘Plochingen’ (Stuttgart), where additionally the alertthreshold (120 ppb as 1-h mean) was surpassedduring 5 h in summer 2001 (Table 5). Our data areconsistent with the evaluation of ozone pollution insummer 2001 published by EEA (2001). There, thenumber of exceedances of information and alertthreshold values increased from zero in Scandinaviato a maximum in central Europe. The Mediterra-nean region showed no consistent spatial pattern,with many stations reporting no exceedances andother stations reporting more than 10. Weatherconditions are important for the occurrence ofprolonged ozone episodes with repeated exceedanceof limit values. In southern European countries,transgression of the information threshold already

ation (days and total number of hours) and of the target value for

permitted by the directive) according to the new Ozone Directive

Alert threshold 120 ppb

(days/hours)

Target value for the

protection of human health

60 ppb (max. 8-h mean)

(days)

0 0

0 0

0 0

0 17

0 35

0 32

0 33

0 21

0 10

0 0

0 0

0 0

0 0

0 2

0 5

0 21

0 34

0 36

0 35

2/5 52

0 63

0 59

0 15

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747972

occurred in April and early May, whereas in centralEurope this threshold was surpassed mostly be-tween June and August. According to EEA (2001),the geographically most extended episode was lateJune (24–27 June), with exceedances in Germany,France, Italy, Benelux countries, Austria, Switzer-land, Czech Republic, northern Spain and evensouthern UK. A so-called anti-episode with noexceedances throughout Europe, by contrast, oc-curred on 16–20 July during a spell of bad weather.Our own data show that most exceedances of thehuman health target and the information thresholdin central Europe (Germany, France, Austria, Italy)occurred during five episodes in late May (23–31/05), late June (21–27/06), late July (22/07–02/08),mid-August (13–18/08), and late August (23–29/08),whereby the onset and duration varied with latitudeand local weather conditions. No exceedances wereregistered during September 2001.

The target value for protection of the vegetation(9000 ppb*h; AOT40 over the period May–July)was exceeded in Klagenfurt, Lyon, Nancy, Stutt-gart, and Verona (Fig. 2 and Table 2). AOT40values above this threshold were mainly registeredat suburban sites, but also occurred at some urbansites in Nancy and Klagenfurt. The highest valuewas 16,173 ppb*h at ‘ZAI’ in Verona, followed by‘Plochingen’ with 15,722 pph*h. The AOT40 valuesfrom suburban sites reported here are comparableto data obtained at rural sites in Austria, Switzer-land or Italy within the UNECE ICP Vegetationnetwork in the same year (Buse et al., 2002). Thehighest value in those studies (29,500 ppb*h) wasregistered in Rome. The AOT40 of 3000 ppb*hdefined as an EU Long-Term Objective and WHOThreshold for the protection of vegetation wassurpassed in all central and southern Europeancities except for Valencia and one site in Barcelona.Even the suburban site ‘Jaegersborg’ in Copenhagensurpassed this limit. Note, however, that the AOT40limit values in the EU Directive are defined as 5-year means in order to compensate for annualvariations, while the statements here are based on asingle study year only. On the other hand, the targetvalues and long-term objectives of the directive referto suburban and rural monitoring stations, whereozone pollution levels are usually higher than nearthe centre. It might actually be questioned whetherit makes sense to apply AOT40, which wasdeveloped as a critical level for crops, for compar-ison of air quality in city centres. Short-term criticallevels aiming to avoid visible injury on sensitive

plant species have been developed recently (PihlKarlsson et al., 2003; UNECE, 2004). However, itmust be emphasised that the AOT40 of 9000 ppb*his currently the only legal threshold in force.

The same sites that exceeded the threshold for theperiod May–July also clearly exceeded the targetvalue of 10,000 ppb*h from April to September forthe protection of forests. Moreover, this thresholdwas nearly reached at suburban sites in Dusseldorfand Barcelona (Table 2). If we consider recent workrecommending an AOT40 value of 5000 ppb*h oreven lower during the growing season to protectsensitive broadleaf and conifer species from harmfulozone effects (Karlsson et al., 2004), then allsuburban sites, except for ‘Lille Valby’ in Copenha-gen, and many urban sites of our network wouldnot meet such a threshold.

4. Conclusions

Photochemical processes regularly lead to ele-vated concentrations of tropospheric ozone in ruraland remote regions of many European countriessurpassing national and European threshold valuesand presumably contributing to vegetation damageand health problems (Buse et al., 2002; EEA, 2003).Our studies conducted in 11 European citiesdemonstrated that current ozone concentrationsare also high enough to jeopardise human healthand vegetation particularly at suburban sites, butalso at some urban sites. The concentrationsmeasured during summer 2001 exceeded the newEuropean target values for the protection of humanhealth at many sites, and thresholds of cumulativeexposure indices established to protect vegetationfrom harmful ozone effects were also surpassed atmany locations. There was a clear gradient withincreasing ozone levels from northern and north-western Europe to central and southern Europeancities; only the Spanish sites did not fit the patterndue to specific local characteristics. Strong ozoneproblems were detected primarily in the cities ineastern and southern France, southern Germany,Austria and northern Italy. This is in agreementwith frequently observed ozone episodes over east-ern France/southwestern Germany and with similarphenomena in the region influenced by the highprecursor emissions from the Po Valley in Italy. Ona local scale, the extent of ozone pollution dependedvery much on the exact location of the monitoringstations. Due to higher NO levels, which helpdestroy photochemically produced ozone, ozone

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–7974 7973

concentrations were significantly lower at urbansites and particularly at strongly traffic-exposedmeasuring stations than at suburban or even ruralstations.

Note that our study assessed data of a single year,whereas the new European target values are to becalculated as multi-annual averages. Moreover,these recently established thresholds shall only bemet in 2010 (or even in 2020 for the long-termobjectives). Otherwise, the year 2001 was a ‘normal’year in terms of meteorological conditions andozone pollution (EEA, 2001) with exception ofScandinavia where unusually low ozone levels wereregistered. In most other countries, values were notas high as in the hot summer 2003, but higher thanduring the relatively wet and cool summer monthsof 2002. Our data support the conclusion that evenin urban areas it will remain difficult to meet thelegal threshold values. The implementation ofmeasures to reduce emissions of precursor sub-stances may lower the risk of short-term peakconcentrations. A future increase of backgroundozone in the northern hemisphere, as assumed byseveral authors (Prather et al., 2003; Grennfelt,2004), however, would aggravate the situation. Thisis particularly true with regard to cumulative indicessuch as AOT40, where even small increases ofbackground levels may strongly increase the num-ber of exceedances.

Acknowledgements

This study was supported by the LIFE Environ-ment Programme of the European Commission,DG Environment, under the Grant LIFE/99/ENV/D/000453. We thank the following local andregional authorities and their respective projectleaders and co-workers for their valuable support:Landeshauptstadt Dusseldorf, Umweltamt (H.-W.Hentze, M. Wiese), Communaute urbaine de Lyon,Ecologie urbaine (O. Laurent), Comune di Verona,Servizio Ecologia (T. Basso, N. Belluzzo, S. Oliboni,S. Pisani, R. Tardiani), The City of EdinburghCouncil, Air Quality Section (T. Stirling), SheffieldCity Council, Environment & Regulatory Services(G. McGrogan, N. Chaplin), LandeshauptstadtKlagenfurt, Abt. Umweltschutz (H.-J. Gutsche),City of Copenhagen, EPA (J. Dahl Madsen),Generalitat de Catalunya, Dept. Medi Ambient,Barcelona (X. Guinart), Communaute Urbaine duGrand Nancy (F. Perrollaz), and Ayuntamientode Valencia, Oficina Tecnica de la Devesa-Albufera

(A. Vizcaino, A. Quintana) as well as the munici-palities of Ditzingen, Plochingen, Deizisau andAltbach (Germany). We acknowledge provision ofdata sets on ambient pollutant concentrations bythe Institute for Physics and Meteorology ofthe University of Hohenheim, Landesanstalt furUmwelt, Messungen und Naturschutz (LUBW)Baden-Wurttemberg, Landesumweltamt (LUA)Nordrhein-Westfalen, Landesregierung Karnten,DMA Generalitat de Catalunya, Airlor Nancy,Coparly Lyon, and EEA AirBase. Gratitude is alsoexpressed to the staff of all institutions involved inthe present studies, and to M. Stachowitsch forproof-reading the English manuscript.

References

Buse, A., Mills, G., Hayes, F., Ashenden, T., and participants of

the ICP Vegetation, 2002. Air pollution and vegetation.

UNECE ICP Vegetation. Annual Report 2001/2002, CEH

Bangor, UK, 55pp.

Coyle, M., Smith, R.I., Stedman, J.R., Weston, K.J., Fowler, D.,

2002. Quantifying the spatial distribution of surface ozone

concentration in the UK. Atmospheric Environment 36,

1013–1024.

De Leeuw, F., 2002. European air quality—past, present and

future. In: Klumpp, A., Fomin, A., Klumpp, G., Ansel, W.

(Eds.), Bioindication and Air Quality in European Cities—

Research, Application, Communication. Heimbach, Stutt-

gart, pp. 19–28.

Duenas, C., Fernandez, M.C., Canete, S., Carretero, J., Liger, E.,

2002. Assessment of ozone variations and meteorological

effects in an urban area in the Mediterranean Coast. The

Science of the Total Environment 299, 97–113.

European Environment Agency (EEA), 2001. Air pollution by

ozone in Europe in summer 2001. Topic Report 13/2001,

Copenhagen, 24pp.

European Environment Agency (EEA), 2003. Europe’s environ-

ment: the third assessment. Environmental Assessment

Report 10, Copenhagen, 343pp.

European Union (EU), 1996. Council Directive 96/62/EC on

ambient air quality assessment and management. Official

Journal of the European Communities 21.11.1996, L296/

55–63.

European Union (EU), 2002. Directive 2002/3/EC of the

European Parliament and of the Council relating to ozone

in ambient air. Official Journal of the European Communities

9.3.2002, L67/14–30.

Fenger, J., 1999. Urban air quality. Atmospheric Environment

33, 4877–4900.

Gangoiti, G., Millan, M.M., Salvador, R., Mantilla, E., 2001.

Long-range transport and re-circulation of pollutants in the

western Mediterranean during the project Regional Cycles of

Air Pollution in the West-Central Mediterranean Area.

Atmospheric Environment 35, 6267–6276.

Garland, J.A., Derwent, R.G., 1979. Destruction at the ground

and the diurnal cycle of concentration of ozone and other

ARTICLE IN PRESSA. Klumpp et al. / Atmospheric Environment 40 (2006) 7963–79747974

gases. Quarterly Journal of Royal Meteorology Society 105,

169–183.

Gimeno, B.S., Penuelas, J., Porcuna, J.L., Reinert, R.A., 1995.

Biomonitoring ozone phytotoxicity in eastern Spain. Water,

Air, and Soil Pollution 85, 1521–1526.

Grennfelt, P., 2004. Recent research findings may change ozone

control policies. Atmospheric Environment 38, 2215–2216.

Karenlampi, L., Skarby, L. (Eds.), 1996. Critical Levels for Ozone

in Europe: Testing and Finalising the Concepts. UNECE

Workshop Report. University of Kuopio, Kuopio, Finland.

Karlsson, P.E., Uddling, J., Braun, S., Broadmeadow, M., Elvira,

S., Gimeno, B.S., Le Thiec, D., Oksanen, E., Vandermeiren,

K., Wilkinson, M., Emberson, L., 2004. New critical levels for

ozone effects on young trees based on AOT40 and simulated

cumulative leaf uptake of ozone. Atmospheric Environment

38, 2283–2294.

Klumpp, A., Ansel, W., Klumpp, G., Belluzzo, N., Calatayud,

V., Chaplin, N., Garrec, J.P., Gutsche, H.-J., Hayes, M.,

Hentze, H.-W., Kambezidis, H., Laurent, O., Penuelas, J.,

Rasmussen, S., Ribas, A., Ro-Poulsen, H., Rossi, S., Sanz,

M.J., Shang, H., Sifakis, N., Vergne, P., 2002. EuroBionet: a

Pan-European biomonitoring network for urban air quality

assessment. Environmental Science & Pollution Research 9,

199–203.

Klumpp, A., Ansel, W., Klumpp, G., 2004. European network

for the assessment of air quality by the use of bioindicator

plants. Final Report, University of Hohenheim, Germany,

168pp. (download from /www.eurobionet.comS).

Klumpp, A., Ansel, W., Klumpp, G., Calatayud, V., Garrec, J.P.,

Shang, H., Penuelas, J., Ribas, A., Ro-Poulsen, H., Rasmus-

sen, S., Sanz, M.J., Vergne, P., 2006a. Tradescantia micro-

nucleus test indicates genotoxic potential of traffic emissions

in European cities. Environmental Pollution 139, 515–522.

Klumpp, A., Ansel, W., Klumpp, G., Vergne, P., Sifakis, N.,

Sanz, M.-J., Rasmussen, S., Ro-Poulsen, H., Ribas, A.,

Penuelas, J., Kambezidis, H., Shang, H., Garrec, J.P.,

Calatayud, V., 2006b. Ozone pollution and ozone biomoni-

toring in European cities. Part II. Ozone-induced plant injury

and its relationship with descriptors of ozone pollution.

Atmospheric Environment, in press, doi:10.1016/j.atmosenv.

2006.07.001.

Mantilla, E., Castell, N., Dieguez, J.J., Palau, J.L., 2002.

Previozono 2001. Programa especial de vigilancia del ozono

troposferico en la Comunidad Valenciana. Fundacion

CEAM, vol. 1, 121pp.

Millan, M.M., Mantilla, E., Salvador, R., Carratala, A., Sanz,

M.J., Alonso, L., Gangoiti, G., Navazo, M., 2000. Ozone

cycles in the Western Mediterranean Basin: interpretation of

monitoring data in complex coastal terrain. Journal of

Applied Meteorology 39, 487–508.

Millan, M.M., Sanz, M.J., Salvador, R., Mantilla, E., 2002.

Atmospheric dynamics and ozone cycles related to nitrogen

deposition in the western Mediterranean. Environmental

Pollution 118, 167–186.

Pihl Karlsson, G., Karlsson, P.E., Danielsson, H., Pleijel, H.,

2003. Clover as a tool for bioindication of phytotoxic ozone—

5 years of experience from southern Sweden—consequences

for the short-term critical levels. The Science of the Total

Environment 301, 205–213.

Prather, M., Gauss, M., Berntsen, T., Isaksen, I., Sundet, J.,

Bey, I., Brasseur, G., Dentener, F., Derwent, R., Stevenson,

D., Grenfell, L., Hauglustaine, D., Horowitz, L., Jacob,

D., Mickley, L., Lawrence, M., von Kuhlmann, R., Muller,

J.-F., Pitari, G., Rogers, H., Johnson, M., Pyle, J., Law,

K., van Weele, M., Wild, O., 2003. Fresh air in the

21st century? Geophysical Research Letters 30 (2), 1100, 72/

1–72/4.

Ribas, A., Penuelas, J., 2003. Biomonitoring of tropospheric

ozone phytotoxicity in rural Catalonia. Atmospheric Envir-

onment 37, 63–71.

Ribas, A., Penuelas, J., 2004. Temporal patterns of surface ozone

levels in different habitats of the North Western Mediterra-

nean basin. Atmospheric Environment 38, 985–992.

Sanz, M.J., Calatayud, V., Sanchez-Pena, G., 2004.

Ozone concentrations measured by passive sampling

at the Intensive Monitoring Plots of South Western Europe.

In: Ferretti, M., Sanz, M.-J., Schaub, M. (Eds.),

Ozone and the Forests of South-West Europe. Final Report,

pp. 51–73.

Tobıas, A., Scotto, M.G., 2005. Prediction of extreme ozone

levels in Barcelona, Spain. Environmental Monitoring and

Assessment 100, 23–32.

Toll, I., Baldasano, J.M., 2000. Modeling of photochemical air

pollution in the Barcelona area with highly disaggregated

anthropogenic and biogenic emissions. Atmospheric Environ-

ment 34, 3069–3084.

United Nations Economic Commission for Europe (UNECE),

2004. Mapping Manual. Mapping Critical Levels for

Vegetation. UNECE ICP Vegetation, Bangor, UK, 53pp.

(Chapter 3).

World Health Organization (WHO), 2000. Air Quality Guide-

lines for Europe, second ed. WHO Regional Office for

Europe, Copenhagen, WHO Regional Publications, Eur-

opean Series, No. 91, 288pp.